Color images are commonly obtained in the silver halide photographic art by reaction between the development product of a silver halide developing agent (e.g., oxidized aromatic primary amine developing agent) and a color forming compound commonly referred to as a coupler. The reaction between the coupler and oxidized developing agent results in coupling of the oxidized developing agent to the coupler at a reactive site on the coupler, known as the coupling position, and yields a dye. The subtractive process of color formation is ordinarily employed in color photographic elements, and the dyes produced by coupling are usually cyan, magenta, or yellow dyes which are formed in or adjacent to silver halide emulsion layers sensitive to red, green, or blue radiation, respectively.
Many couplers well known for forming yellow dyes contain an open-chain ketomethylene group in the coupling moieties. One class of such couplers comprises acylacetanilides, such as pivalylacetanilides and benzoylacetanilides, described, for example, in U.S. Pat. Nos. 2,407,210; 3,265,506; 3,408,194; 3,894,875; and 4,157,919.
However, such known couplers often have drawbacks.
One such drawback is that silver halide photographic elements containing such couplers often exhibit lower than desirable photographic speed. That is, the elements require exposure to larger than desirable amounts of actinic radiation to finally yield a given level of dye image density.
Another common drawback of many acylacetanilide couplers is the relatively low level of maximum density (Dmax) and/or contrast yielded by the yellow dyes formed from such couplers in silver halide photographic elements.
A further common drawback is the relatively high equivalent weight of many yellow-dye-forming couplers. The term, "equivalent weight", as used herein is equal to the molecular weight of the coupler divided by the number of efficiently reactive coupling moieties in the coupler molecule. Each efficiently reactive coupling moiety is capable of reacting with oxidized developing agent to form a colored dye moiety. The higher the equivalent weight of the coupler is, the larger is the mass of coupler that must be included in a photographic element layer in order to be able to produce the desired amount of developed image dye optical density. The need for a larger mass of coupler in a layer results in a thicker layer, which inherently reduces the transparency and optical sharpness of the layer. Thus, lower equivalent weight couplers allow for thinner, more transparent, optically sharper layers. Unfortunately, the overall mass of a coupler molecule must be relatively large in order to provide sufficient organic ballast to properly suspend the coupler molecules in droplets of high boiling organic liquid, referred to as coupler solvent, which are dispersed in the desired layer of the photographic element, and thereby anchor the coupler in the layer and prevent it from diffusing to adjacent layers or out of the element during processing with various aqueous processing liquids. Thus, the needs for lower equivalent weight and sufficient organic ballast are at apparent cross-purposes.
Also, some characteristics of acylacetanilide yellow-dye-forming couplers, in addition to their coupling speeds and efficiencies and their molecular and equivalent weights, can be significantly affected by the nature of any particular substituents that may be bonded to the coupling moieties at positions other than the coupling position, because such substituents remain bonded to the dye moieties formed by the coupling reaction. For example, it is known that the nature of such substituents can significantly affect the hue of the dye moieties and their mobility in a photographic element. Relatively immobile yellow dyes tend to provide images of higher granularity and higher sharpness, while more mobile yellow dyes can migrate slightly (often referred to as "smearing") to provide reduced granularity and lower sharpness. The desired combination of hue and balance of granularity and sharpness may be different for various photographic elements, depending upon their intended uses.
There is therefore a continuing need for a new class of yellow-dye-forming couplers that can minimize the drawbacks described above, i.e., that can be incorporated in silver halide photographic elements without causing lower than desirable photographic speed, that can form yellow dyes in silver halide photographic elements that yield relatively high levels of maximum density (Dmax) and contrast, and that have relatively low equivalent weight, while at the same time having relatively high molecular weight to provide sufficient organic ballast for proper incorporation and anchoring in photographic element layers. It would also be desirable for such a new class of couplers to provide the flexibility to choose among various different substituents to have at positions on the coupling moieties other than the coupling position, in order to be able to tailor the effects of such substituents (effects such as described above) to meet particular needs in various photographic elements. Of course, the couplers should also exhibit all the other characteristics desirable for good photographic performance.